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Sinclair ZX Spectrum

The British 8-bit icon (1982): a Z80, a single ULA doing video + I/O, and a colossal library. Standard Sinclair repair: the ULA (heat-fragile), the lower RAM, the regulator and the membrane keyboard.

ZX Spectrum (1982)

ZX Spectrum (1982) — photo by Jzh2074, CC BY-SA 4.0 (Wikimedia Commons).

Identification / models

Model Year RAM Note
16K / 48K ("rubber keys") 1982 16/48 KB rubber keys, ULA
48K+ 1984 48 KB revised keyboard
128 ("toastrack") 1985 128 KB AY-3-8912 sound, memory banks
+2 (grey) / +2A (black) 1986-87 128 KB built-in tape deck
+3 1987 128 KB 3″ disk drive (like Amstrad)

CPU Z80 @ 3.5 MHz; video 256×192, 15 colours with the signature "attribute clash".

Repair (technician)

The ULA — the emblematic fault

The ULA (Ferranti) generates video and I/O; it runs hot and fails (no/corrupt picture, crashes). Cool it (heatsink), and as a last resort replace it (used ULA or a modern replacement like nu-ULA/vLA82).

  • Lower RAM (16 KB): 4116 DRAM (needs +5/+12/−5 V) → faulty = checkerboard / crash; substitution. The upper (48K) RAM is 4164.
  • 7805 regulator ("black guardsman"): runs hot → heatsink/ventilation; external 9 V supply.
  • Membrane keyboard: the No. 1 usage fault → replacement membrane (new ones available).
  • +2A/+3: mains RIFA in the PSU (smoke) → replace; 3″ drive (+3) = belt.
  • Video output: composite/RF stock → RGB/SCART mods (video mods).

Original service manual ✅

Manufacturer manual archived locally. It typically carries the schematics, the block diagram, the expected voltages and waveforms, the parts list and the disassembly procedures — the reference when a symptom matches no known fault.

  • ZX Spectrum 128 — service manual — PDF

Status

A manufacturer document with no explicit licence, kept for preservation (machine long out of production) — the same position as for the cabinet and arcade manuals already archived here. Source: Internet Archive.

Common faults

Symptom Likely cause Lead
No / corrupt picture ULA / lower RAM Cool/replace ULA, substitute 4116
Checkerboard at boot lower RAM (4116) Substitute the DRAM
Dead keys keyboard membrane Replace the membrane
Reset / crashes when hot ULA / regulator Heatsink, recap
Smoke (+2A/+3) mains RIFA Replace the RIFA

Modernisation & mods — what to buy, how

Fragile parts: ULA, low RAM, membrane keyboard

The #1 weak point is the ULA (runs hot, dies) → a reissued modern ULA (vLA / Nebula) as a substitute. The 4116 RAM (low 16/48K bank) often fails → identify by test and substitute. The membrane keyboard cracks → a remade membrane. A modern regulated PSU is recommended.

Modern storage - DivMMC (Enjoy!) / DivIDE + ESXDOS 🟢: an SD card on the rear expansion port → instant loading (plug-and-play); Kempston SD interfaces. - Floppy +2A/+3 🟡: Gotek + FlashFloppy (internal drive connector, images from USB).

Video - The RF output is poor → a composite mod 🟡, or better an RGB mod 🟠 (RGB tapped from the ULA) → SCART then OSSC / RetroTINK / RGB2HDMI.

Reliability: light recap; clean the connectors.

⚠️ Do not host ROMs/games — method only.

See also

Sources & attribution

Review & corrections

How this space is used

Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.

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